Hi Danny
The fact that you are asking about this type of work shows that you are serious about your business. At the same time it suggests that you are lacking in experience and/or training.
Belgian Wiltons in this environment is rare. I presume that you have little experience of the scenario you've described, so you must firstly be prepared to walk away from this potentially lucrative job if you can't tick all the right boxes.
Firstly, you must spend a lot of time on your inspection. The industry recommendation is that BW's are fitted on architectural gripper, if not a double row of conventional gripper. Look at the sub floor. Is the gripper exceptionally secure, or are there areas where the gripper is lifting? even by a small amount? If it's a concrete floor, are the right nails used? If glued, is the gripper cut into 3 or 4" strips or just glued down as single longer pieces? If a wooden floor, are the right nails used? The wrong combination can result in shrinkage, and boy, can BW's shrink
Was the carpet a stretch fit or loose laid on the grippers? It should have been a loose lay and tucked in without stretching. If the carpet is tight now, it will probably shrink even from a pre-spray.
There are other considerations too, like seams/joins, but with BW's, if the fit is immaculate, then it should be safe to proceed with an LM/bonnet system.
I presume that you have satisfied yourself that the carpet is a polypropylene pile with a high jute content woven construction? Anything else, and it's not a Belgian Wilton.
In the commercial environment, even more so than residential, there are serious H&S consequences should a carpet shrink or split a seam. DO NOT PROCEED if you are not confident.
Safe and happy cleaning
Ken